Battery management systems are known that employ controllable switches for disconnecting or otherwise isolating batteries from external circuits when one or more of the batteries are subject to certain fault or non-fault battery conditions. In a conventional battery management system involving a single battery, such a controllable switch is typically connected in series with the single battery. Further, a discharging circuit or a charging circuit can be formed by connecting a load or a charging voltage source, respectively, across the series-connected battery and controllable switch. In the event of a certain fault or non-fault battery condition, the controllable switch can be transitioned from a closed or “ON” state to an opened or “OFF” state, thereby disconnecting the battery from the discharging circuit or the charging circuit of which the battery was a part. For example, in a discharging circuit, such a battery condition might result from the battery being fully discharged or having its temperature exceed a preset limit. In a charging circuit, such a battery condition might result from the battery being fully charged or experiencing thermal runaway.
In such a conventional system involving a single battery, when the single battery is disconnected from the discharging circuit by the controllable switch, the switch can experience a voltage of up to the maximum voltage of the battery when fully charged. Further, when the single battery is disconnected from the charging circuit by the controllable switch, the switch can experience a voltage of up to the difference between the charging voltage and the battery voltage. To avoid having the switch experience a voltage in excess of its voltage rating (i.e., the maximum voltage that the switch can tolerate while in the opened or OFF state), the switch is typically selected such that its voltage rating can (a) accommodate the maximum battery voltage when it is used to disconnect the battery from the discharging circuit, or (b) accommodate the maximum charging voltage when it is used to disconnect the battery from the charging circuit.
In another conventional battery management system involving multiple batteries, such a controllable switch can be connected in series with each of the respective batteries, and the series-connected batteries and controllable switches can, in turn, be connected in series. Like the conventional system involving a single battery, a discharging circuit or a charging circuit can be formed by connecting a load or a charging voltage source, respectively, across all of the series-connected batteries and controllable switches. In the event of a certain fault or non-fault battery condition, one of the controllable switches connected in series with the respective batteries can be transitioned from the closed or ON state to the opened or OFF state, thereby disconnecting the multiple batteries from the discharging circuit or the charging circuit of which the batteries were a part.
In such a conventional system involving multiple batteries, when the multiple batteries are disconnected from the discharging circuit by one of the controllable switches, the switch can experience a voltage of up to the sum of the voltages of all of the respective batteries. Further, when the multiple batteries are disconnected from the charging circuit by the respective switch, the switch can experience a voltage of up to the difference between the charging voltage and the sum of the voltages of all of the respective batteries. As with the conventional system involving the single battery, to avoid having a switch experience a voltage in excess of its voltage rating, each switch is typically selected such that its voltage rating can (a) accommodate the sum of the maximum voltages of all of the respective batteries when it is used to disconnect the multiple batteries from the discharging circuit, or (b) accommodate the maximum charging voltage when it is used to disconnect the multiple batteries from the charging circuit.
The conventional battery management systems described herein have several drawbacks, however. For example, the cost of the controllable switches employed in such conventional systems generally increases in proportion to the voltage rating of the respective switches, potentially making such switches prohibitively expensive for some battery management applications. Further, such switches that have increased voltage ratings typically exhibit a relatively high internal series resistance, which can result in increased losses and reduced efficiency, as well as the need for costly thermodynamic mitigations in the system design. In addition, in the conventional system that involves multiple batteries, the number of batteries employed in the system can be limited by the voltage rating of the controllable switches selected for use therein, due at least in part to the increased cost of such switches having high voltage ratings.
It would therefore be desirable to have improved systems and methods of providing integrated battery protection for series-connected batteries that avoid at least some of the drawbacks of the conventional battery management systems described herein.